Device for making porous concrete

ABSTRACT

Device for making of porous concrete intended for casting of e.g. elements of buildings, by which mainly cement, water and a frothing agent are mixed at the same time causing air pores in the mixture to be clasted, consisting of a cylindrical mixing-tank (1) in which an impeller (3) is arranged with a rotation axis which coincides with the center axis of the mixing-tank (1) and by which the impeller (3) includes blades (31) that extend helicoidally along the mixing tank (1) by which the helicoidally of each blade is less than 90° over the length of the impeller (3) and by which the blades (31) extend a bit against the center axis of the impeller (3). Each blade (31) consists of two, in direction to the center axis of the impeller (3), reciprocally flat strips (32), which incline against the envelope to the mixing tank (1) so that the front edge in the moving direction of the outer strip (32) is located next to the envelope. Wings (33 ) are arranged between the strips (32) in each blade which incline against the center axis of the impeller (3).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for making of porous concreteintended for casting purposes, e.g., for casting portions of buildingssuch as foundation plates, walls and beams wherein principally cement,water and a frothing agent are simultaneously mixed in a way that airpores are produced in the mixture.

2. The Prior Art

A known method for making porous concrete involves mixing cement, sand,and water in a concrete mixer, after which a separately produced frothis lead into and mixed in the concrete. The concrete mixer constitutedby a stationary tank having a rotating mixing screw or similar elementtherein. The froth is produced by a device in which a frothing agent ismixed with air and eventually water so that a froth with small airbubbles is obtained. A device for producing such a froth is described inthe Swedish Patent Publication No. 156215.

In order to obtain a uniform quality of the cast porous concrete, i.e.,such that it has a uniform density and strength, it is required that theincluded raw material be mixed in the right proportions. With continuousproduction, this has been found to be difficult as careful measurementof the flows of raw material and a watching of the mixing times.Further, an effective mixing of the air is required in order not tooverly extend the mixing time.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for makingporous concrete which is easier to use than known devices and whichensures that a uniform and high quality of the cast porous concrete isachieved. According to the invention the device enables all raw materialto be mixed in batches, which means that the raw material can be addedin exact quantities. Further, it includes control equipment in the formof a micro-computer by which the mixing time and other mixing parameterscan be kept equal for all batches during one and the same casting. Thedevice consists of a cylindrical mixing tank in which an impeller isarranged so that its axis of rotation coincides with the centre axis ofthe tank, and wherein the impeller includes blades that extendhelicoidally along the inner envelope surface of the tank, by which thehelicoidallity of each blade is less than 90°, preferably 40°, over thelength of the tank and by which the blades extend a bit against thecentre axis of the impeller.

Each blade preferably consists of two, in direction to the centre axisof the impeller, reciprocally parallel, flat strips which inclineagainst the envelope of the mixing tank, so that the front edge of themoving direction of the outer strip is located next to the envelope.Between the strips, wings are arranged, by which respective wing islocated in a plane which inclines against the centre axis of theimpeller. Further, propeller blades preferably are arranged along thecentre axis, which extend a bit from the centre axis. The bladespreferably are supported by arms, which extend from the centre axis ofthe impeller and which carry a propeller blade each.

A great advantage with the device in accordance with the presentinvention is that all raw material can be prepared in one and the sameapparatus. As such, there is no need for a special device for producingof froth, instead it is prepared at the same time as the porousconcrete. This circumstance also has raised other demands on the designof the device compared with the known devices for making of porousconcrete by putting in a prefabricated froth into concrete mixer.

Surprising it has been proved that the characteristics of the inventionare deciding in order to carry out the preparation in the one and thesame device and obtain an uniform quality of porous concrete besides theadvantages that are reached by the batch-wise preparation which isdescribed above. The turbulence which is obtained in the mixture by theblades of the impeller and propeller blades provides a good mixing ofthe air which is in the tank to provide a porous concrete with uniformlyspread pores. The device in accordance with the invention alsoconstitutes a very compact unit which can be easily transported from oneplace to another, e.g., it can be easily mounted on a vehicle. Noextensive training of operating personnel is needed, indeed it can beused by anybody (it can be rented to users, for example).

The invention will be beter understood by reference to the attacheddrawings, taken in conjunction with the following discussion.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a side view of a concrete mixer according to a preferredembodiment of the present invention.

FIG. 2 shows a schematic view of an impeller for the mixer shown in FIG.1.

FIG. 3 shows the impeller in accordance with FIG. 2 as seen in thedirection of the rotation axis.

FIG. 4 schematically shows a blade of the impeller in accordance withFIGS. 2 and 3 as seen from one side.

FIG. 5 shows the blade in accordance with FIG. 4 as seen from above.

FIG. 6 shows a cross-section of the blade in accordance with FIG. 4along the line 6--6.

FIG. 7 shows a view over a blade in accordance with FIG. 6 along theline 7--7.

FIG. 8 shows a cross-section of an impeller in accordance with FIG. 4along the line 8--8, the hub of the impeller also being shown.

FIG. 9 shows the detail in accordance with FIG. 8 as seen from above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a device according to a preferred embodiment of theinvention includes a cylindrical mixing tank 1 which is arranged with aninclining centre axis on a stand 2. The mixing tank 1 has an impeller 3mounted therein such that its axis of rotation coincides with the centreaxis of the tank. The impeller is rotated by a motor 4 which isconnected to the impeller 3 at the upper gable of the tank 1. At the topof the upper gable of the tank 1 a water tank 5 is affixed and connectedto the mixing tank 1 by a water conduit 6 having a cut-off valve 7. Alsoin direct connection with the water tank 5 are two tanks 8,9 forfrothing emulsion, these tanks being connected to the mixing tank 1 byemulsion conduits 10,11 having cut-off valves 12,13. A funnel 14 forcement is arranged at the top of the envelope of the mixing tank 1 andsurrounded by a stand 15 on which a transport container, shown dashed atFIG. 1, is placed at filling up. Downwards at the lower gable of themixing tank, a pump 16 is arranged for pumping the prepared porousconcrete mixture by a flexible hose 17 to the place where the casting isto be carried out. Controlling and watching of the mixing procedure isdone by help of control equipment arranged in a locker 18 arranged indirect connection to the mixing tank 1.

The impeller 3 comprises four blades 31, which extend helicoidally alongthe inner envelope surface of the mixing tank 1, by which thehelicoidallity in accordance with the example is 45° over the length ofthe impeller 3 and by which the blades 31 extend a bit against thecentre axis of the impeller 3. The helicoidallity is arranged againstthe direction of rotation which is marked with an arrow in FIG. 2.Further, the left gable of the impeller 3 in accordance with FIG. 2, isarranged at the upper gable of the mixing tank 1 in accordance withFIG. 1. Each blade 31 consists of two, in direction to the centre axisof the impeller, reciprocally parallel, flat strips 32 which areinclined with respect to against the envelope of the mixing tank 1, sothat the front edge in the moving direction of the outer strip 32 islocated next to the envelope. More specifically, each strip 32 isinclined 15° with respect to the tangent to the rotation circle throughthe front edge of each strip 32. Between the strips 32, wings 33 arearranged, each wing 33 extending in a plane that is inclined withrespect to the centre axis of the impeller 3. The plane through eachwing 33 inclines 15° with respect to a plane extending at a right angleto the centre axis of the impeller 3, by which the front edge of eachwing 33 is located next to the left cable of the impeller 3, which inits turn is located at the upper gable of the mixing tank 1. The blades32 are supported by arms 34, which extend from the centre axis of theimpeller 3. Four arms 34 are arranged on a hub 35 in a plane at a rightangle to the centre axis of the impeller and in reciprocally rightangles. Further, at the same hub 35, four propeller blades 36 arearranged which each extend parallel to each arm 34. Each propeller blade36 is inclined 15° with respect to a plane at a right angle to thecentre axis of the impeller 3, by which the front edge of each blade 36in the same way as the corresponding front edge of the wings 33 in theblades 31 as mentioned above.

During preparation of a porous concrete mixture for casting, a cementcontainer containing a determined amount of cement is placed on thestand 15 on top of the mixing tank 1. The watertank 5 and the emulsiontanks 8,9 are filled up with water and with respective emulsions inproportions corresponding to the amount of cement. The cement after thatis manually pulled down into the mixing tank 1 by the funnel 14. Afterthat the control equipment is switched on, by which the valve 7 at thewater conduit 6 is opened, causing water to flow into the mixing tank 1.The rotation of the impeller 3 is started and is kept running for adetermined time, after which the control equipment opens the valve 12 inthe emulsion conduit 10 from the first emulsion tank 8. The running ofthe impeller 3 is maintained for a determined time, after which thecontrol equipment opens the valve 13 in the emulsion conduit 11 from thesecond emulsion tank 9. After another determined time of running of theimpeller 3, the porous concrete mixture is ready and can be pumped tothe location for casting by the pump 16 at the lower end of the mixingtank 1 and by the flexible hose 17, which is connected to the pump 16.

I claim:
 1. A device for mixing cement, water and a frothing agent inorder to provide a porous concrete for casting, said device comprisingacylindrical mixing tank which defines a central axis line therethroughand which has an interior surface that defines a mixing chamber therein,and an impeller rotatably mounted in said mixing chamber within saidcylindrical mixing tank, said impeller having a central axle whichcoincides with said central axis line of said cylindrical mixing tank,said impeller including a plurality of elongated blades that extendhelicoidally with respect to said central axle of said impeller andadjacent said interior surface of said cylindrical mixing tank, eachsaid blade consisting of first and second curved strips which extend inparallel to one another, said second strip being located radiallyoutwardly of said first strip, said second strip being inclined alongits length less than 90° with respect to the adjacent interior surfaceof said cylindrical mixing tank, said second strip having along itslength a side edge which is adjacent said interior wall of saidcylindrical mixing tank.
 2. A device as defined in claim 1, wherein eachblade of said impeller includes a plurality of flat wings extendingbetween the first and second curved strips thereof, each wing extendingin a plane which is inclined with respect to a plane extendingtransversely with respect to said central axle.
 3. A device as definedin claim 1, wherein said impeller includes a plurality of hubs mountedon said central axle, a plurality of support arms which extend radiallyoutwardly from each said hub, each support arm supporting a respectiveblade thereon, and a plurality of flat propeller blades which extendradially away from each hub, each said flat propeller blade extending ina plane which is inclined relative to a plane perpendicular to saidcentral axle.
 4. A device as defined in claim 1, wherein thehelicoidally of each blade is less than 90° around the circumference ofsaid impeller.